Antimicrobial Silver Nanoclusters Bearing Biocompatible Phosphorylcholine-Based Zwitterionic Protection

Infection is one of the most serious issues in medical treatments leading to the development of several antimicrobial agents. In particular, silver ions released from silver substrates is well-known as a reliable antimicrobial agent that either kills the microorganisms or inhibits their growth. Unfortunately, many reports have shown that silver-based antimicrobial agents are toxic for human cells as well. To improve the biocompatibility of silver antimicrobial agents, we have synthesized thiol-terminated phosphorylcholine (PC-SH)-protected silver nanoclusters (PC–AgNCs) via strong thiol–metal coordination with controlled ultrasmall size of the clusters. A change in plasmon-like optical absorption was studied to affirm the successful synthesis of small thiolated AgNCs through the absorption spectra that become molecular-like for the AgNCs. We observed that PC–AgNCs were spherical with an average diameter of <2 nm. The ultrasmall size clusters were exceedingly immobilized by the PC-SH on the surface, resulting in excellent biocompatibility and antibacterial activity simultaneously. The biocompatible, antimicrobial PC–AgNCs exhibit interesting advantages compared with other silver antimicrobial agents for medical applications

Patterned Poly(acrylic acid) Brushes Containing Gold Nanoparticles for Peptide Detection by Surface-Assisted Laser Desorption/Ionization Mass Spectrometry

Patterned poly­(acrylic acid) (PAA) brushes was successfully generated via photolithography and surface-initiated reversible addition–fragmentation chain transfer (RAFT) polymerization of acrylic acid as verified by water contact angle measurements and FT-IR analysis. The carboxyl groups of PAA brushes can act as reducing moieties for in situ synthesis of gold nanoparticles (AuNPs), without the use of additional reducing agent. The formation of AuNPs was confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy. The glass surface-modified by PAA brushes and immobilized with AuNPs (AuNPs-PAA) can be used as a substrate for SALDI-MS analysis, which is capable of detecting both small peptides having <i>m</i>/<i>z</i> ≤ 600 (glutathione) and large peptides having <i>m</i>/<i>z</i> ≥ 1000 (bradykinin, ICNK­QDCP­ILE) without the interference from matrix signal suggesting that AuNPs were stably trapped within the PAA brushes and the carboxyl groups of PAA can serve as internal proton source. By employing AuNPs as the capture probe, the AuNPs-PAA substrate can selectively identify thiol-containing peptides from the peptide mixtures with LOD as low as 0.1 and 0.05 nM for glutathione and ICNK­QDCP­ILE, respectively. An ability to selectively detect ICNK­QDCP­ILE in a diluted human serum is also demonstrated. The patterned format together with its high sensitivity and selectivity render this newly developed substrate a potential platform for high-throughput analysis of other biomarkers, especially those with low molecular weight in complex biological samples

Optical Properties of 2‑Methacryloyloxyethyl Phosphorylcholine-Protected Au₄ Nanoclusters and Their Fluorescence Sensing of C‑Reactive Protein

We present the solution synthesis of thiolated 2-methacryloyloxyethyl phosphorylcholine (MPC)-protected Au nanoclusters (NCs). This water-soluble lipid-mimetic MPC was first used for the size focusing synthesis of thiolate (SR)-protected Au_<i>n</i>(SR)_<i>m</i> NCs. Au₂₅(MPC)₁₈ and Au₄(MPC)₄ NCs are selectively synthesized, without the need for electrophoretic or chromatographic isolation of size mixed products, by including ethanol or not in the solvent. The Au₄(MPC)₄ NCs emit at yellow wavelengths (580–600 nm) with a quantum yield (3.6%) and an average lifetime of 1.5 μs. Also for the first time, we report C-reactive protein (CRP) sensing using Au NCs, with a detection limit (5 nM) low enough for the clinical diagnosis of inflammation. This is based on the quenching effect of specific CRP–MPC interactions on the fluorescence of the Au₄(MPC)₄ NCs